Our laboratory examines HIV replication in highly relevant primary cell systems to more closely mimic viral infection in vivo. In contrast to many laboratories working with similar primary cell systems, our research employs molecular virological tools within this context. We thus have been able to derive new insights into the interactions of HIV with immune system cells, and in particular, to identify previously unrecognized cellular factors that play important roles in virus replication. We are interested in extending these analyses in vivo, working in both murine and rhesus macaque model systems to better understand the contribution of cell factors to virus replication and immune pathogenesis. Primary Cell Transmission of HIV A great deal of the initial research on HIV replication in vitro employed examination of "lab-adapted" viral isolates cultured on transformed cell lines. While this work has been enormously useful in our understanding of HIV and its interactions with T cells, in many circumstances it has also been misleading and uninformative about the larger picture of immune pathogenesis due to the inherent limitations of these systems and the differences in the biology of transformed cells relative to primary cells. Thus, we have calibrated our analyses to look at cells and cell culture conditions that more closely resemble the in vivo environment in which HIV infection and immune depletion occur. Some of our recent work has involved characterization of how primary dendritic cells transmit HIV to CD4+ T cells, which has revealed new targets for possible therapeutic intervention. Indeed, we have developed neutralizing antibodies that block this transmission process in vitro. Dendritic cells have been postulated as key players in the sexual/mucosal transmission of HIV; thus, an understanding of their role in this process may directly aid prevention of the spread of HIV. Animal Models for HIV Infection We have invested significant effort toward understanding why murine immune system cells, particularly the CD4+ T cells, are refractory to HIV infection. This analysis has led to the description of human cofactors that are required by HIV for productive infection (and whose mouse counterparts are nonfunctional with regard to HIV). There are two benefits that could be derived from these analyses. In the short term, they may reveal human cellular factors that are required by HIV for its reproductive cycle and that might, therefore, be targets for novel drug therapies. Second, this information allows us to further genetically manipulate the mouse to increase its susceptibility to HIV infection. Given that mice possess an immune system even better defined than that of humans and one that is similar to humans, with an HIV-susceptible mouse one would conceivably be able to gain new insights into the interactions of the pathogen and the immune system that are beyond our reach in the current models. Finally, in addition to our work on murine systems, we are currently involved in research using the rhesus macaque model to examine strategies to prevent mucosal transmission of virus based on our studies with primary cells in vitro.